The present invention is related to a window arrangement on a pressure pipe, preferably for the vulcanisation or crosslinking of sheathings of electric cables.
In the manufacture of cables, the cable sheathing is extruded on the cable core with the aid of an extruder. By crosslinking the cable coating consisting of plastic material, the plastic mass is made elastic. The crosslinking or vulcanisation, respectively, of the plastic material takes place in a pressure pipe, in which there are relatively high temperatures and a significant overpressure, for instance temperatures up to 550° C. and pressures up to 30 bars.
It is known to determine the diameter of cable sheathing and/or the thickness of individual layers of the cable sheathing with the aid of an x-ray measurement device. The x-ray measurement device features an x-ray radiation source and an x-ray sensitive receiver. The latter is for instance made up of individual x-ray sensitive elements, which are sensed in series.
When a determination of wall thickness and/or diameter of a cable is to be performed during its passage through the pressure pipe, the x-ray measurement device must be arranged in the train of the pressure pipe. It is known to use separate casings for this, which are aligned to diametrically opposing passages in the pressure pipe, through which the measurement plane of the x-ray measurement device extends perpendicularly to the longitudinal axis of the pressure pipe. The passages are sealingly closed by a window plate, which is easily transmissive for x-rays.
It is known to provide thin window plates made of beryllium. Of the metals, beryllium has the lowest absorption of x-rays, at equal values of strength. The beryllium plates are fixed against a shoulder in the passage together with a flat seal, namely by a projection of a so-called T-flange, which is fastened on the casing on the outside by screwing. The beryllium plate is pressed against a passage shoulder via the seal under high pressure with the aid of the T-flange.
Beryllium is considered to be highly toxic, and beryllium dust is carcinogenic.
For this reason and in order to improve the corrosion resistance of the beryllium plates, the same are overlaid with a ceramic layer for instance. During the operation in the pressure pipe, condensate accumulates in the lower region of the beryllium window, and together with sulphur- and chlorine containing components it causes corrosion of the beryllium. Carcinogenic beryllium particles can reach the operation control region when beryllium plates become permeable by corrosion pressure and are ejected into the atmosphere through this. Ceramic and also metal coatings of the beryllium plate in order to avoid corrosion have proven to be effective only in a limited extent, because of too small layer thicknesses.
It is also known to arrange a protective foil before the beryllium plate for protection purposes. Like a coating, the same can be damaged when solid residues which had been precipitated on the beryllium foil are being removed.
Finally, in the conventional arrangement of beryllium plates a sumptuous examination of the placement of the seals is necessary after the installation, in particular in order to avoid a leakage, because in such cases beryllium particles could arrive in the air of the surroundings.
The present invention is based on the objective to provide a window arrangement on a pressure pipe, preferably for the vulcanisation or crosslinking of sheathings of electric cables, which is less prone to corrosion and permits a drain-off of the condensate.